This document has three purposes. First, the compendium aims to help Head Start managers and other early childhood education administrators review information regarding the reliability and validity of commonly used assessment and developmental screening tools in order to help them better select appropriate tools for the populations they serve. Second, the compendium aims more generally to increase awareness about reliability and validity and how to evaluate whether an instrument is reliable and valid for the population and purpose for which it will be used. Finally, the compendium aims to highlight areas in which the early childhood field is lacking information on reliability and validity of early childhood assessments and developmental screeners. While originally developed in response to Head Start's reauthorization, the compendium is designed to be useful to managers and staff who work in different types of early childhood education programs and who are responsible for selecting and evaluating assessment or screening instruments. (author abstract)